diff --git a/examples/client.c b/examples/client.c
index 6329ab3f..e391079b 100644
--- a/examples/client.c
+++ b/examples/client.c
@@ -86,6 +86,7 @@ coap_new_request( method_t m, coap_list_t *options ) {
     return NULL;
 
   pdu->hdr->type = COAP_MESSAGE_CON;
+  pdu->hdr->id = rand();	/* use a random transaction id */
   pdu->hdr->code = m;
 
   for (opt = options; opt; opt = opt->next) {
@@ -95,6 +96,8 @@ coap_new_request( method_t m, coap_list_t *options ) {
   }
   
   if (payload.length) {
+    /* TODO: must handle block */
+
     coap_add_data(pdu, payload.length, payload.s);
   }
 
diff --git a/net.c b/net.c
index 7a6bdde2..ffccfa5e 100644
--- a/net.c
+++ b/net.c
@@ -305,12 +305,8 @@ coap_send_impl( coap_context_t *context, const struct sockaddr_in6 *dst, coap_pd
   return ntohs(pdu->hdr->id);
 }
 
-#define create_transaction_id(T) do { T = (unsigned short)rand(); } while ( T == COAP_INVALID_TID );
-
 coap_tid_t
 coap_send( coap_context_t *context, const struct sockaddr_in6 *dst, coap_pdu_t *pdu ) {
-  if ( ntohs(pdu->hdr->id) == COAP_INVALID_TID )
-    create_transaction_id( pdu->hdr->id );
   return coap_send_impl( context, dst, pdu, 1 );
 }
 
@@ -323,9 +319,6 @@ coap_tid_t
 coap_send_confirmed( coap_context_t *context, const struct sockaddr_in6 *dst, coap_pdu_t *pdu ) {
   coap_queue_t *node;
 
-  if ( ntohs(pdu->hdr->id) == COAP_INVALID_TID )
-    create_transaction_id( pdu->hdr->id );
-
   /* send once, and enter into message queue for retransmission unless
    * retransmission counter is reached */
 
diff --git a/pdu.h b/pdu.h
index 939a97a8..df1141af 100644
--- a/pdu.h
+++ b/pdu.h
@@ -95,8 +95,9 @@
 #define COAP_MEDIATYPE_ANY                         0xff /* any media type */
 
 /* CoAP transaction id */
-typedef unsigned short coap_tid_t; 
-#define COAP_INVALID_TID 0
+/*typedef unsigned short coap_tid_t; */
+typedef int coap_tid_t; 
+#define COAP_INVALID_TID -1
 
 #ifndef BYTE_ORDER
 #  if (BSD >= 199103)